1. Field of the Invention
The present invention relates generally to printing presses and more particularly to a printing unit including control device for automatically moving a tucker bar away from its operating position and a method for plating a plate cylinder using such a control device.
2. Background Information
Offset lithographic printing presses, for example, have a plate cylinder and a blanket cylinder for transferring images from a printing cylinder to a web of material, such as paper.
A flat printing plate typically is attached to the plate cylinder via an axially-extending gap. The lead edge of the plate is inserted in the gap, and the plate cylinder is rotated, so that a plate-to-blanket nip forces the plate to wrap around the plate cylinder. A tucker bar than is used to tuck the tail edge of the plate into the axially-extending gap.
U.S. Pat. No. 6,439,117, for example, which is hereby incorporated by reference herein (and is which is not necessarily prior art to the present invention), discloses a tucker bar.
In order to provide access to the plate cylinder for inserting the lead edge, tucker bars typically have been moved manually away from the plate cylinder into a non-operating position where they cannot tuck the tail edge. This can be a time-consuming operation.
An object of the present invention is to provide a device and method for automatically moving a tucker bar to aid in plating a printing press.
The present invention provides a printing unit with a plate cylinder having an axially-extending gap. A tucker bar has an operating position, the tucker bar in the operating position capable of tucking a tail end of a printing plate into the axially-extending gap. A tucker bar control device automatically moves the tucker bar away from the operating position to a non-operating position.
The printing unit may further include a frame supporting the plate cylinder and tucker bar with the tucker bar control device being attached to the frame. The tucker bar control device may include an eccentric cam, which may be rotated, for example, using a pneumatic motor.
During the plating process, it may be necessary to run the press in the forward and reverse directions to adjust the position of the axially-extending gap on the plate cylinder. Preferably, the tucker bar in the operating position is located at a nip between the plate cylinder and a blanket cylinder to guard the nip and to provide improved safety when the web is rolling in the forward direction. Also, the tucker bar can advantageously be moved to non-operating position located at a nip between two blanket cylinders to guard the nip and to provide improved safety when the web is rolling in the reverse direction.
The tucker bar control device may also include a lever operationally connected to the tucker bar and the tucker bar control device to enable manually moving the tucker bar from an operating to a non-operating position for cleaning and maintenance.
The invention further provides a method for plating a plate cylinder. A tucker bar control device is used to automatically move a tucker bar from an operating position to a non-operating position so as to permit access to an axially-extending gap in the plate cylinder. A lead end of a printing plate is inserted into the axially-extending gap.
The method may include moving the tucker bar from a position in which it guards a nip between the plate cylinder and an adjacent blanket cylinder in the operating position. Also, the method may include moving the tucker bar to a position in which it guards a nip between the adjacent blanket cylinder and a second blanket cylinder in the non-operating position.
The control device aids in permitting an operator to access the plate cylinder for improved plating without having to manually move the tucker bar, resulting in a significant saving of time and effort.